Seasonal variation in lipid and fatty acid composition of ice algae from the Barents Sea

The fatty acid compositions of neutral lipid, glycolipid and phospholipid fractions from ice algae sampled from the Barents Sea in spring and autumn were examined for seasonal differences. The ice-algal assemblages were dominated by diatoms. In spring, Nitzschia frigida was the most common species whereas resting stages of Thalassiosira bioculata and Actinocyclus cf curvatulus predominated in autumn. With the exception of one spring sample, neutral lipids predominated over glycolipids and phospholipids in all algal samples. The lipid fractions displayed characteristic fatty acid compositions. In the spring samples the major fatty acids of the neutral lipid fraction were 16:0, 16:1(n-7) and 20:5(n-3) whilst the glycolipid fraction was characterised by higher levels of 20:5(n-3) and C16 polyunsaturated fatty acids, particularly 16:4(n-1). Phospholipids contained higher levels of 22:6(n-3) than the other two lipid fractions although 20:5(n-3) was still the major polyunsaturated fatty acid. In the autumn samples, the neutral lipid fraction contained higher proportions of saturated fatty acids and 16:1(n-7) than the two polar lipid fractions and 22:6(n-3) was most abundant in phospholipids. As with the spring samples, 20:5(n-3) was the major polyunsaturated fatty acid in all lipid fractions of the autumn algae. Overall, the fatty acid compositions of the lipid fractions from spring and autumn algal samples were similar and are consistent with diatoms being the predominant group in the ice algae studied. The high level of neutral lipids observed in both spring and autumn samples suggests that the production of neutral lipids is characteristic of ice algae regardless of season. Nevertheless, some species-specific differences in lipid production may exist since the neutral lipid content of autumn samples containing mainly A. curvatulus was substantially higher than those in which T. bioculata predominated. Received: 26 September 1997 / Accepted: 12 January 1998     

Metal concentrations in Sargassum algae from coastal waters of Nha Trang Bay (South China Sea)

The concentrations of metals, viz., Fe, Mn, Cu, Zn, Cd, Pb, and Ni, were investigated in brown algae of the genus Sargassum collected in the coastal waters of Nha Trang Bay (South China Sea). Metal concentrations in algae growing in the zone of influence of the city of Nha Trang were higher than those in macrophytes collected to the south and north of the city. Similar levels of Cu and Fe concentrations were observed in macrophytes from the urbanized coastal areas of Nha Trang Bay and in algae from the Peter the Great Bay (Sea of Japan). This is suggestive of comparable metal inputs from the anthropogenic sources of the cities of Nha Trang and Vladivostok (Peter the Great Bay). However, the concentrations of Pb, Ni, and Cd in algae from the coastal waters of Nha Trang Bay were lower than in macrophytes from the inshore zone of Vladivostok. The high level of pollution of sea water with Zn compounds near Nha Trang was local. The metal levels in macrophytes from background areas reflect the geochemical features of the environment. Sargassum algae from Nha Trang Bay had lower concentrations of Zn, Cd, and Ni and higher concentrations of Mn than algae from Peter the Great Bay. The background concentrations of Cu, Pb, and Fe in macrophytes from both bays were virtually the same.     

Diurnal variation of cell proliferation in three bacterial taxa from coastal North Sea waters

Pulse-labeling with bromodeoxyuridine (BrdU) in combination with fluorescence in situ hybridization was applied to quantify the percentage of proliferating cells in coastal North Sea waters. In order to assess diurnal variability, we sampled eight or nine times, respectively, within 3 consecutive days at two seasons. Bacteria affiliated with the Roseobacter, SAR86, and NOR5 lineages constituted on average 19% +/- 3%, 8% +/- 2%, and 6% +/- 1% of all cells in May 2002 and 17% +/- 3%, 10% +/- 2%, and 11% +/- 3% in August. The relative abundances of the three populations either remained stable, or they changed very gradually during the observation periods. On average, 38 and 39% of all Bacteria exhibited DNA de novo synthesis in May and August, respectively. The fractions of proliferating cells in bacteria of the SAR86 (May, 59%; August, 72%) and the Roseobacter (48 and 53%) lineages were significantly above the community average. A substantial cell proliferation of population NOR5 (34%) was only encountered in August, concomitant with a dinoflagellate bloom. Significant short-term fluctuations of DNA-synthesizing cells were observed in Roseobacter during May and in NOR5 during August, hinting at a pronounced (temporal or spatial) mesoscale patchiness of growth rates in these populations. Since the BrdU proliferation assay is susceptible to misinterpretation, we also modeled the expected number of labeled cells at increasing BrdU incubation times in a slowly growing bacterial population. We suggest that the absence of visible DNA synthesis in marine bacterioplankton cells after DNA pulse-labeling must not be interpreted as an indication of cell "inactivity."     

Seasonal patterns in the sunlight sensitivity of bacterioplankton from Mediterranean surface coastal waters

The sensitivity of coastal marine bacterioplankton to natural photosynthetically active radiation (PAR, 400-700?nm) and ultraviolet radiation (UVR, 280-400?nm) was evaluated in five experiments over a seasonal cycle in the Blanes Bay, NW Mediterranean Sea. Exposure to natural solar radiation generally inhibited bulk bacterial activities or damaged membrane integrity when irradiances were high (i.e. spring and summer experiments) and, in general, UVB (280-320?nm) accounted for most of the inhibition. When assessing activity ((3) H-leucine uptake) at the single-cell level by microautoradiography and rRNA gene probing, seasonally varying responses and sensitivities were found among bacterial groups. While autumn and winter irradiances seemed too low to cause changes in activity, variable effects were found in spring and summer. SAR11 was consistently inhibited by UVR and PAR exposure, whereas Gammaproteobacteria and Bacteroidetes showed higher resistance. Roseobacter, Synechococcus and the NOR5 clade were occasionally photostimulated in their activity, mainly because of PAR. Our results indicate that a component of seasonality exists in the bacterial responses to solar radiation, which vary not only depending on the irradiance and the spectral characteristics, but also on the previous light history and the taxonomic composition of the community.     

Enrichment of omnivorous cercozoan nanoflagellates from coastal Baltic Sea waters

Free-living nano-sized flagellates are important bacterivores in aquatic habitats. However, some slightly larger forms can also be omnivorous, i.e., forage upon both bacterial and eukaryotic resources. This hitherto largely ignored feeding mode may have pronounced implications for the interpretation of experiments about protistan bacterivory. We followed the response of an uncultured group of omnivorous cercozoan nanoflagellates from the Novel Clade 2 (Cerc_BAL02) to experimental food web manipulation in samples from the Gulf of Gdańsk (Southern Baltic Sea). Seawater was either prefiltered through 5 μm filters to exclude larger predators of nanoflagellates (F-treatment), or prefiltered and subsequently 1∶10 diluted with sterile seawater (F+D-treatment) to stimulate the growth of both, flagellates and bacteria. Initially, Cerc_BAL02 were rapidly enriched under both conditions. They foraged on both, eukaryotic prey and bacteria, and were highly competitive at low concentrations of food. However, these omnivores were later only successful in the F+D treatment, where they eventually represented almost one fifth of all aplastidic nanoflagellates. By contrast, their numbers stagnated in the F-treatment, possibly due to top-down control by a concomitant bloom of other, unidentified flagellates. In analogy with observations about the enrichment of opportunistically growing bacteria in comparable experimental setups we suggest that the low numbers of omnivorous Cerc_Bal02 flagellates in waters of the Gulf of Gdańsk might also be related to their vulnerability to grazing pressure.     

Seasonal variation in plankton, submicrometre particles and size-fractionated dissolved organic carbon in Antarctic coastal waters

Concentrations of plankton, suspended particles 0.74–87 μm equivalent spherical diameter and dissolved organic carbon (DOC) were measured from May to February at an Antarctic coastal site. Bacteria-sized particles 0.74–1 μm diameter, and bacterial cells and heterotrophic protists all exhibited a seasonal minimum during winter and maxima in summer. Bacteria composed <10% of the bacteria-sized particles. Release of autotrophic protists from the ice caused water column biomass of autotrophs to reach maximum concentrations in October and November, but maximum cell concentration in the water column was reached in January. Microheterotroph biomass weakly reflected the release of the ice algal community but reached maximum concentration during the water column bloom in January. Total DOC concentrations varied from 0.36 mg C l⁻¹ in July to 3.10 mg C l⁻¹ in October, with a yearly average of 1.51 mg C l⁻¹. Ultrafiltration of DOC revealed that the molecular weight composition of the DOC differed greatly through the year. DOC <5 kDa molecular weight reached a maximum of 1.25 mg C l⁻¹ in October and accounted for up to 60% of total DOC in July. Concentrations of high molecular weight DOC (>100 kDa) were highest in July and November, with the DOC (100 kDa–0.5 μm) fraction reaching a maximum of 1.22 mg C l⁻¹ in November and composing 82% of the total DOC in January. Wet chemical oxidation and high-temperature catalytic oxidation organic carbon analyses were compared. Good correlation was observed between methods during summer but no significant correlation existed in winter, indicating that winter DOC may be refractory. Accepted: 21 March 2000     

Seasonal population dynamics and trophic role of planktonic nanoflagellates in coastal surface waters of the Southern Baltic Sea

We investigated the temporal dynamics and trophic role of different nanoflagellates in surface waters of the Gulf of Gdańsk (Baltic Sea) between April and October 2007. Two 18S rRNA gene clone libraries were constructed from samples collected in spring and summer, and weekly changes in the abundances of five phylogenetic groups were studied by fluorescence in situ hybridization with newly designed probes. Stramenopiles affiliated with MAST‐6 and Pedinellales were most numerous in spring but rare in summer. Both groups formed short‐lived blooms during a sudden drop of salinity due to riverine influx (from 7.1 to 6.2 practical salinity units). The analysis of food vacuole content suggested that MAST‐6 nanoflagellates were herbivorous, whereas bacterivory was found both in plastidic and aplastidic pedinellid populations. Members of an uncultured lineage of aplastidic, bacterivorous cercozoans distantly related to Ebria tripartita were more abundant in summer when water temperatures exceeded 17°C. Multicellular trophonts and/or free‐living single cell stages of two lineages of Group 1 parasitic Syndiniales (alveolates) were present in spring and early summer. One of these alveolate populations repeatedly peaked before and after the freshwater influx, but was conspicuously absent throughout the period of decreased salinity. Our results indicate that nanoflagellate populations in coastal surface waters may form short‐lived blooms that can only be detected by high‐frequency sampling, and that may be related both to seasonal development and to sporadic (e.g. mixing) events. In view of their trophic diversity we moreover suggest that nanoflagellates in eutrophic coastal waters should not be regarded as a single functional unit.     

Seasonal, genetic and age variation in non-esterified fatty acid concentrations in the ewe

Plasma samples were collected at intervals of about 2 weeks from about ten 2 1/2 year old, or older, and five 1 1/2 year old ewes of each of the Scottish Blackface, Finnish Landrace and Tasmanian Merino ewes and were assayed for their non-esterified fatty acid (NEFA) concentrations. The NEFA concentrations showed an increase with time for every animal. The NEFA concentrations and their linear increase was least in the Finnish Landrace animals. The increase with time was greatest in the Merinos. There was no difference between the age groups. There was no evidence of any annual, cyclical trend.     

Annual cycle of nanophytoplankton in coastal waters of the Barents Sea

The seasonal dynamics of biomass and size structure of nanophytoplankton in Central Murman (off the southern coast of the Barents Sea) are described according to the results of six-year continuous observations. The pattern of the annual successional cycle indicates that the nanophytoplankton community as a structural unit of coastal pelagic algocenoses is a specific integrated ecological group of primary producers. The issue of a major contribution of nanoalgae to the total biomass and production of the autotrophic component of coastal ecosystems in Arctic seas is discussed.     

Seasonal variation in the diet of South African Galagos

The feeding behavior and diet of two species of bushbaby, Galago senegalensisand Galago crassicaudatus,in South Africa were examined in relation to seasonal changes in climate. The populations studied were allopatric, but both fed predominantly on Acaciagum and invertebrates. Data on their diet were collected by direct observation of a radiocollared female of each species and by analysis of fecal samples. Differences in diet were found between the species within seasons and within species between the seasons. Both spent more time gum-feeding in winter than in summer. Prey size and type differed between the species in summer but converged in winter. The quantity of insects taken was fairly similar between seasons for G. senegalensisbut dropped considerably for G. crassicaudatusin winter. These observations are interpreted in terms of interspecific differences in feeding strategies, which are considered to be a function of the difference in body size of the two galago species.     

Seasonal variation in the phosphatase activity of waters and sewage sludges

Summary The alkaline phosphatase activity of water from eight locations differing in orthophosphate concentration has been determined over a period from late Autumn to late Summer. Evidence for induction/repression effects was conjectural, but cellular activity was highest in the environment of lowest orthophosphate concentration. Environments were sampled on a number of occasions and pH/phosphatase activity profiles constructed. The pH of maximum activity of low phosphate environments was in the acid region, that of high phosphate environments was in the alkaline region. There was little difference in the character and distribution of constitutive phosphatases in representative bacterial cultures from a high phosphate and a low phosphate environment. It seems likely that the phosphatase activity of a water at a particular time will be influenced by its nutrient and physico-chemical status as well as its ambient orthophosphate concentration.     

Diversity and abundance of ammonia-oxidizing prokaryotes in sediments from the coastal Pearl River estuary to the South China Sea

In the present study the diversity and abundance of nitrifying microbes including ammonia-oxidizing archaea (AOA) and betaproteobacteria (beta-AOB) were investigated, along with the physicochemical parameters potentially affecting them, in a transect of surface sediments from the coastal margin adjacent to the Pearl River estuary to the slope in the deep South China Sea. Nitrifying microbial diversity was determined by detecting the amoA (ammonia monooxygenase subunit A) gene. An obvious community structure shift for both AOA and beta-AOB from the coastal marginal areas to the slope in the deep-sea was detected, while the OTU numbers of AOA amoA were more stable than those of the beta-AOB. The OTUs of beta-AOB increased with the distance from the coastal margin areas to the slope in the deep-sea. Beta-AOB showed lower diversity with dominant strains in a polluted area but higher diversity without dominant strains in a clean area. Moreover, the diversity of beta-AOB was correlated with pH values, while no noticeable relationships were established between AOA and physicochemical parameters. Beta-AOB was more sensitive to transect environmental variability and might be a potential indicator for environmental changes. Additionally, the surface sediments surveyed in the South China Sea harboured diverse and distinct AOA and beta-AOB phylotypes different from other environments, suggesting the endemicity of some nitrifying prokaryotes in the South China Sea.     

Seasonal variation of natural products in European trees

The present review gives an overview about the status of research on seasonal variation of natural products in European trees. Due to their different life forms, gymnosperms, deciduous angiosperms, and evergreen angiosperms are reviewed separately. Besides trying to give an overview about the existing newer literature, the review tries to define some repetitively found trends and discusses some possible explanations for these trends. Moreover, open research questions are highlighted and some suggestions for future studies are given. These suggestions encompass both subjects and desirable quality standards with regards to experimental designs. The reviewed publications are mainly focused on leaves, some on fruits, and some on barks and twigs. Phenolics, including phenolic acids and flavonoids of different types as well as tannins, are the most often studied compound class; additionally, some papers assess seasonal variation of alkaloids, diterpenes, essential oils, lignans, simple organic acid, secoiridoids, and stilbenoids.     

Seasonal and spatial diversity of microbial communities in marine sediments of the South China Sea

This study was conducted to characterize the diversity of microbial communities in marine sediments of the South China Sea by means of 16S rRNA gene clone libraries. The results revealed that the sediment samples collected in summer harboured a more diverse microbial community than that collected in winter, Deltaproteobacteria dominated 16S rRNA gene clone libraries from both seasons, followed by Gammaproteobacteria, Acidobacteria, Nitrospirae, Planctomycetes, Firmicutes. Archaea phylotypes were also found. The majority of clone sequences shared greatest similarity to uncultured organisms, mainly from hydrothermal sediments and cold seep sediments. In addition, the sedimentary microbial communities in the coastal sea appears to be much more diverse than that of the open sea. A spatial pattern in the sediment samples was observed that the sediment samples collected from the coastal sea and the open sea clustered separately, a novel microbial community dominated the open sea. The data indicate that changes in environmental conditions are accompanied by significant variations in diversity of microbial communities at the South China Sea.     

Seasonal variation in triacylglyceride fatty acids of dwarf mistletoes

Fatty acids in the triacylglyceride fraction of three species of dwarf mistletoe (Arceuthobium, Viscaceae) showed considerable seasonal variation in proportions of saturated acids and some differences in chain length for those fatty acids. Early summer aerial shoot tissue contained 34–49% saturated fatty acids, while the same species in late October had only 8–15% saturated fatty acids. Fatty acids with a chain length of C₂₀ or greater comprised 18–25% of the total in late June but only 1.5–6.4% in the autumn. Three other species analysed in only one season showed similar saturated fatty acids, and chain length patterns were also parallel to the seasonally varying species analysed in the same season. The ratio of linolenic to oleic acid remained constant with season but linolenic acid increased from less than 1% in June to 7–8% in October samples.